This study is designed to investigate the hypothesis that drugs with a faster rate of onset produce greater euphoria, and therefore constitute a greater risk for abuse, than drugs with a slower onset. In this study, 12 subjects will participate in 3 weekly sessions in which they will receive intravenous infusions of diazepam (slow or rapid) or placebo. Subjective effects (e.g., euphoria) and behavioral effects (e.g. psycho-motor impairment) of the drug will be compared under the slow and rapid conditions.